Tube Rows Research Articles

복합 전열 촉진 핀이 적용된 핀-관 열교환기의 성능에 대한 실험적 연구

Abstract In this study, heat transfer and friction characteristics of compound enhanced fin-and-tube heat exchangerswere experimentally investigated. Louver-finned heat exchangers were also tested for comparison purpose. The effectof fin pitch on j and f factor was negligible. The j factor decreased as number of tube row increased. However, ffactor was independent of number of tube row. Louver fin samples yielded higher j and f factors than compoundenhanced fin samples. For one row, j and f factors of louver fin were 23% and 27% higher than those of compoundenhanced fin. For two row, those were 11% and 8%, and for three row, those were 10% and 9%. However, heat transfer capacities at the same pressure drop of the compound enhanced fins were 6.4% for one row, 11.1% for tworow and 13.6% for three row larger than those of louver fins, Existing louver fin correlation overpredicted the presentj factors and underpredicted the present f factors. Keywords : Compound enhanced fin, Heat transfer coefficient, Louver fin, Pressure drop

비대칭형 슬릿 핀이 적용된 핀-관 열교환기의 습표면 성능

Abstract In this study, wet surface heat transfer and friction characteristics of non-symmetric slit-finned heat exchangers are experimentally investigated. Louver-finned heat exchangers are also tested for comparison purpose. Theeffect of fin pitch on j and f factor is negligible. Louver fin samples yield higher j and f factors than slit fin samples. For one row, j and f factors of louver fin are 27% and 31% higher than those of slit fin. For two row, j and f factors of louver fin are 15% and 30% higher. Both j and f factor decrease as the number of tube row increases. For onerow, average j/f ratios of slit fin samples are 3.4% larger than those of louver fin samples. For two row, average j/f ratios of slit fin samples are 11.5% larger. A new correlation was developed using the present data. Key Words : Heat transfer coefficient, Pressure drop, Slit fin, Wet surface * Corresponding Author : Nea-Hyun Kim (Incheon National Univ.) Tel: +82-032-835-8420 email: knh0001@incheon.ac.krReceived February 3, 2015 Accepted June 11, 2015Revised (1st March 20, 2015, 2nd April 1, 2015)Published June 30, 2015

Experimental investigation on performances of trisection helical baffled heat exchangers for oil/water–water heat transfer

The trisection helical baffled shell-and-tube heat exchangers have structural features of more suitable to the equilateral triangular tube layouts and less baffle parts. In particular the circumferential overlap trisection helical baffled shell-and-tube heat exchangers are of anti-shortcut structure that accommodates one row tubes in each circumferential overlapped zone between adjacent baffles for dampening shortcut leakage. The performance tests were conducted on both oil–water and water–water heat transfer in heat exchangers with equilateral triangle tube layout of 16 tubes including five helical baffle schemes with incline angles of 12°, 16°, 20°, 24°, 28° and a segmental baffled one for comparison. The test results show that both the shell side heat transfer coefficient ho and pressure drop Δpo increase but the comprehensive index ho/Δpo decreases with the increase of the mass flow rate of all schemes; and that the shell side heat transfer coefficient, pressure drop and the comprehensive index ho/Δpo decrease with the increase of the baffle incline angle at certain mass flow rate, except that the curves of comprehensive index ho/Δpo of 12° and 16° helical baffle schemes are almost coincide. The average values of shell side heat transfer coefficient, the comprehensive index ho/Δpo of the 12° helical baffled scheme are about 50% higher than those of the segmental one with almost same pressure drop. The correlation equations for shell side Nusselt number and axial Euler number are presented varying with axial Reynolds number, Prandtl number and helical baffle incline angle.

Performances of helical baffle heat exchangers with different baffle assembly configurations

The flow and heat transfer characteristics of helical baffle heat exchangers with diverse inclined angles and baffles, but similar baffle pitch and tube layout, were numerically simulated, three using non‐continuous trisection baffles, two using non‐continuous quadrant baffles, and one using a continuous helical baffle. The results show that, under the same operating conditions, the 20°TCO (trisection circumferential overlap baffles with 20° inclined angle) structure can significantly enhance shell side heat transfer with strong Dean vortex “secondary flow“ and restrained V‐notch leakage, because the shapes of trisection baffles are very suitable to equilateral triangle tube layout and there is a row of tubes to dampen the leakage flow in each circumferential overlapped area of adjacent baffles. The shell side Nusselt Number Nuo and comprehensive index (Nuo/Euz,o1/3) of 20°TCO structure are 18.31 %, 25.82 %, 5.93 %, 6.36 %, and 15.04 %, and 15.43 %, 18.47 %, 5.30 %, 3.91 %, and 11.10 % higher than those of the 20°TEE (trisection end‐to‐end baffles with 20° inclined angle), 36.2°TMO (trisection middle overlap baffles with 36.2° inclined angle), 18°QCO (quadrant circumferential overlap baffles with 18° inclined angle), 18°QEE (quadrant end‐to‐end baffles with 18° inclined angle), and 18.4°CH (continuous helical baffle with 18.4° helical angle) structures, respectively.

Air-side performance of serrated welded spiral fin-and-tube heat exchangers

Heat exchanger is a basic component used in thermal processes such as industrial fluid heating, household appliances, waste heat recovery units (WHRU), etc. Presently, the spiral fin-and-tube heat exchanger is used as a favored type of heat exchanger for the waste heat recovery unit system, i.e., the economizer heat exchanger. The study investigates the effect of fin pitches on the air-side performance of serrated welded spiral fin-and-tube heat exchangers having Z-shape flow arrangement and the number of tube rows of 2 in range of high Reynolds numbers (4000–15,000). The test samples are made from steel (iron) with different fin pitches of 3.6, 4.2, and 6.2mm. The experimental results reveal that the fin pitch has a significant effect on the air-side performance. It is confirmed that the fin pitch of 3.6–6.2mm has the same trend in heat transfer coefficient at the tested condition. For f-friction factor, a detectable rise of the friction factor is found when the fin pitches increase to 6.2mm. Moreover, the air-side performance correlations of serrated welded spiral finned tube heat exchangers are proposed for practical industrial applications. The proposed air-side performance correlation describes 100% for j-Colburn factor and f-friction factor within 10%.

Integration of Genetic Programing With Genetic Algorithm for Correlating Heat Transfer Problems

In the present paper, the genetic programing (GP) is integrated with the genetic algorithm (GA) for deriving heat transfer correlations. In the process of developing heat transfer correlations with the approach (GP with GA (GPA)), the GP is first employed to obtain some potential optimal forms. After that, the forms are further optimized with the global GA to reach minimum errors between the predicted values and experimental values. With the proposed approach, three typical different heat transfer problems are applied to the data reduction processes from published experimental data, which are heat transfer in a shell-and-tube heat exchanger (STHE) with continuous helical baffles, a single row heat exchanger with helically finned tubes and a finned oval-tube heat exchanger with double rows of tubes, respectively. The results indicate that the GPA approach could improve the performance of heat transfer correlations obtained with the GP. Compared with the power-law-based correlations, the heat transfer correlations obtained with the approach have higher predicted accuracies and more excellent robustness.

Heat Transfer and Pressure Drop Characteristics of Plain Fin-and-Tube Heat Exchangers Having 5.0 mm Tubes Under Dehumidifying Condition

In this study, wet surface pressure drop and heat transfer characteristics of plain finned heat exchangers having 5.0 mm diameter (5.3 mm after tube expansion) tubes were investigated. Nine samples having different fin pitches (1.1 to 1.3 mm) and tube rows (1 to 3 rows) were tested. The fin pitch had a negligible effect on j and f factors. Both j and f factors decreased as the number of tube row increased. When compared the j and f factors of the samples having 5.3 mm diameter tubes with those of 7.3 mm diameter tubes, 5.3 mm samples yielded higher j factors and lower f factors. The j/f ratios of 5.3 mm samples are larger than those of 7.3 mm samples which implies that 5.3 mm geometry is more beneficial than 7.3 mm geometry.

An Experimental Investigation on the Airside Performance of Fin-and-Tube Heat Exchangers Having Nonsymmetrical Slit Fins

In this study, the heat transfer and friction characteristics of nonsymmetric slit-finned heat exchangers are experimentally investigated. Louver-finned heat exchangers are also tested for comparison purpose. The effect of fin pitch on j and f factors is negligible. Considering the small variation of the fin pitch (from 1.3 mm to 1.5 mm), the foregoing argument should hold true for the present samples. Louver fin samples yield higher j and f factors than slit fin samples. Both j and f factors increase as the number of tube rows decreases. The row effect is true for both slit and louver fin samples. For one-row configuration, j/f ratios of louver fin samples are larger than those of slit fin samples. The trend is, however, reversed for three-row configuration. Data are compared with available correlations.

БИОНИЧЕСКИЕ ПРИНЦИПЫ ОПТИМИЗАЦИИ ТЕПЛО- И ХЛАДОПРОВОДОВ

Bionic approach to create technological devices based on the fact that a number of ideas and the basic elements of the device borrowed from living nature. In this case, it is postulated that over millions of years of evolution in living nature have already been found optimal solutions, which require only a correct interpretation. As a prototype of heat or cold conduits in living nature, taking into account the analogy between heat and mass transfer, select the root system of plants. In morphology root system of plants is divided into two types: fibrous root system type and taproot system. In accordance with these two types of heat reviewed: branched and unbranched. An algorithm for optimizing the shape and size of heating conduits. Received an analytical expression allowing to evaluate the warm-up time unbranched heat conductor and the maximum temperature that can be achieved in electric heating heat conductor. On the example of the longitudinal tube riffles forming atmospheric evaporators high pressure branched were optimized of heating conduits. The choice of the optimal form of ribs for chess and in-line tube bank. For staggered multiple rows of tubes is the best ribs in the form of snowflakes. For in-line tube bank proved optimal ribs with four diagonal ribs.

Performance Comparison of Trisection Helical Baffle Heat Exchangers with Different Circumferential Overlap Sizes

AbstractThe circumferential overlap structure is considered as one of the key factors which influence the performances of helical baffle heat exchangers by restraining the bypass stream between adjacent baffles. The flow and thermal performances of four trisection helical baffle heat exchangers with the same angle of inclination but different circumferential overlap sizes were numerically investigated. The four schemes involve an end‐to‐end one and three circumferential overlap ones with triangular area covering one row (20°TCO), two rows (20°T2CO), and three rows (20°T3CO) of tubes. The flow field and combined slices with pressure contours plus velocity vectors were depicted. The 20°TCO scheme proved to be superior to other schemes since its Nusselt number as well as its comprehensive index are the highest and its secondary flow is the strongest.

Experimental study on heat transfer characteristics of water-spray-bed heat exchanger

An experimental study was conducted on a water-spray-bed heat exchanger to investigate the heat transfer characteristics. A laboratory-scale test rig was built and its heat transfer characteristics were investigated with respect to various design and operation parameters such as the water spray flow rate, exhaust gas flow rate and number of tube rows. It was found that the implementation of the water spray increased the heat transfer rate to about 1.3 - 2.2 times that of a heat exchanger without water spray, although with a slight increase in the pressure loss. It was thus confirmed that the water spray was effective for enhancing condensing heat recovery from an exhaust gas.

Determination of fin pitches for maximum performance index of L-footed spiral fin-and-tube heat exchangers

In this study, the fin pitches of L-footed spiral finned tube heat exchangers were determined for maximimum performance index. The experiments were done at various fin pitches ( fp = 2.4, 3.2, and 4.2 mm) under the range of high Reynolds numbers (5,000–15,000). The test sections had a parallel and counter cross-flow arrangement having the number of tube row of 2. The two working fluids were the ambient air and hot water. The performance indexes ( ζ1, ζ2, and ζ3) were used to analyze the experimental data at different fin pitches. The results show that the optimal fin pitches for L-footed spiral finned tube heat exchangers are 2.4 and 3.2 mm.

A review on the thermal hydraulic characteristics of the air-cooled heat exchangers in forced convection

In this paper, a review is presented on the experimental investigations and the numerical simulations performed to analyze the thermal-hydraulic performance of the air-cooled heat exchangers. The air-cooled heat exchangers mostly consist of the finned-tube bundles. The primary role of the extended surfaces (fins) is to provide more heat transfer area to enhance the rate of heat transfer on the air side. The secondary role of the fins is to generate vortices, which help in enhancing the mixing and the heat transfer coefficient. In this study, the annular and plate fins are considered, the annular fins are further divided into four categories: (1) plane annular fins, (2) serrated fins, (3) crimped spiral fins, (4) perforated fins, and similarly for the plate fins, the fin types are: (1) plain plate fins, (2) wavy plate fins, (3) plate fins with DWP, and (4) slit and strip fins. In Section 4, the performance of the various types of fins is presented with respect to the parameters: (1) Reynolds number, (2) fin pitch, (3) fin height, (4) fin thickness, (5) tube diameter, (6) tube pitch, (7) tube type, (8) number of tube rows, and (9) effect of dehumidifying conditions. In Section 5, the conclusions and the recommendations for the future work have been given.

사인 웨이브 핀과 타원관으로 구성된 핀-관 열교환기의 공기측 습표면 성능

본 논문은 12.7mm 원관을 변형하여 만든 세장비 0.6(짧은 직경 10.0mm, 긴 직경 16.5mm)의 타원관이 적용된 사인 웨이브 핀-관 열교환기의 습표면 공기측 성능실험에 관한 것이다. 핀 핏치와 열 수를 변화시켜 총 12개의 시료에 대하여 실험을 수행하였다. 타원관에서 핀 핏치 변화에 따른 j, f 인자의 영향은 미미 하였으나, 열수에 따라서는 1row에서 j인자가 가장 낮았다 (가장 높은 2row의 81%). 하지만 원관에서는 1row에서 가장 높게 나타나는 차이점을 보였다. 이는 타원관에 적용된 사인 웨이브 채널의 유동 특성에 기인한 것으로 판단된다. 원관 열교환기와 $j/f^{1/3}$ 값을 비교한 결과 1열을 제외하고는 타원관 열교환기의 전열성능이 우수함을 알 수 있다. 즉, 타원관 열교환기의 $j/f^{1/3}$ 값이 원관의 값보다 2열에서 1.6~2.5 배, 3열에서 1.4~2.4 배, 4열에서 1.2~1.8배 크게 나타났다. 【Experiments were conducted on sine wave fin-and-tube heat exchangers having oval tubes under wet condition. Oval tubes having an aspect ratio of 0.6 were made, by deforming 12.7mm round tubes. Twelve samples, having different fin pitch and tube row, were tested. Results showed that, for oval tube samples, the effect of fin pitch on j and f factor was not significant. As for the effect of tube row, the lowest j factor was obtained for one row configuration(81% of two row configuration), which is clear contrast to round tube samples, where the highest j factor was obtained for one row configuration. Possible reasoning is provided considering the flow and heat transfer characteristics of sine wave channel combined with connecting oval tubes. Comparison of $j/f^{1/3}$ with plain fin-and-tube heat exchanger having 15.9mm O.D. round tube reveals that present oval fin-and-tube heat exchanger shows superior thermal performance except for one row configuration. In other words, $j/f^{1/3}$ of the two row oval tube heat exchanger was 1.6~2.5 times larger than those of round tube heat exchanger, 1.4~2.4 times larger for three row configuration and 1.2~2.8 times for four row configuration.】

Thermo-economic optimisation of industrial milk spray dryer exhaust to inlet air heat recovery

This study reports a thermo-economic design optimisation of an industrial milk spray dryer liquid coupled loop exhaust heat recovery system. Incorporated into the analysis is the ability to predict the level of milk powder fouling over time and its impacts on heat transfer and pressure drop. Focus is given to a finned round tube, a bare round tube and a bare elliptical tube. Modelling results show that spray exhaust heat recovery is economically viable for the considered industrial case study. Based on the results, the best liquid coupled loop heat exchange system uses a finned tube heat exchanger to recover heat from the exhaust air with a face velocity of 4 m/s and 14 tube rows, which gives a net present value of NZ$2.9 million and an internal rate of return of 71%. The developed thermo-economic assessment method has the ability to cater to site specific needs that affect the utility savings and the capital cost for implementing exhaust heat recovery.

Numerical study of the effect of fouling on local heat transfer conditions in a high-temperature fin-and-tube heat exchanger

The paper presents the numerical analysis of a flow around a bundle of externally finned elliptical tubes, used in cross-flow heat exchangers of a flue-gas/water type, arranged serially in two rows. An algorithm that enables determining the variations of flue-gas temperature and local heat transfer coefficient from gas to the tube wall was presented. On the basis of calculations, it was found that the intensity of heat transfer processes differs significantly in different rows. The intensity is higher in the first row and lower in the second one. This fact is confirmed by the values of the local heat transfer coefficients calculated for the case of heat transfer from gas to a wall determined at the same location. The coefficients, calculated for the first row of tubes, are higher compared with those of the second row. The appearance of fouling deposits on the tube's wall inner surface has an impact on the average temperature along the exhaust gas flow path. It also affects the local heat transfer coefficients from the gas-side to the tube walls. The presence of fouling increases the flue-gas temperature, while its influence on the heat transfer coefficient is slight.

Mathematical modeling and control of plate fin and tube heat exchangers

The aim of the study is to develop a new method for numerical modeling of tubular cross-flow heat exchangers. Using the method proposed in the paper, a numerical model of a car radiator was developed and implemented in a digital control system of the radiator. To evaluate the accuracy of the numerical method proposed in the paper, the numerical model of the car radiator was compared with an analytic model. The proposed method based on a finite volume method and integral averaging of gas temperature across a tube row is appropriate for modeling of plate fin and tube heat exchangers, especially for exchangers in which substantial gas temperature differences in one tube row occur. The target of control is to regulate the number of fan revolutions per minute so that the water temperature at the heat exchanger outlet is equal to a set value. Two control techniques were developed. The first is based on the numerical model of the heat exchanger developed in the paper while the second is a digital proportional–integral–derivative control. The first control method is very stable. The digital proportional–integral–derivative controller becomes unstable when the water volume flow rate varies considerably. The developed techniques were implemented in digital control system of the water exit temperature in a plate fin and tube heat exchanger. The measured exit temperature of the water was very close to the set value of the temperature if the first method was used. The experiments show that the proportional–integral–derivative controller works also well but becomes frequently unstable if the water flow rate varies.

3D numerical analysis of exhaust flow inside a fin-and-tube evaporator used in engine waste heat recovery

A fin-and-tube evaporator can be used for an ORC (organic Rankine cycle) to collect waste heat of the exhaust gas of an internal combustion engine. In this paper, the thermal-hydraulic characteristics of an ORC evaporator are analyzed using a CFD method. A 3D numerical model is derived from an engineering diagram of the fin-and-tube evaporator, and the boundary conditions are specified according to the measured data obtained by the engine test. The simulation results show that the exhaust on the shell side flows primarily parallel with the fin layers. Alternating high and low temperatures appear on the middle planes of the adjacent tube rows. The shapes of the front-end and the rear-end parts connecting the main body to the exhaust pipes are important factors on the flow field. The maximum exhaust pressure decrease in the fin-and-tube evaporator is significantly less than the backpressure limit required by the engine exhaust pipe. The simulation results are verified by an engine experiment, and there exists a correlation between the numerical results and the actual heat transfer process.

Importance of Location & Alignment of Geotextile Tubes for the Coastal Protection Measures

The placement of the geotextile tubes plays a functional role in the performance of the overall protection scheme. The placement path of geotextile tubes is the crucial decision for the designers. The geotextile tubes are widely used as a reef structure, well below the Mean Sea Level. The requirement of the beach width is the main criterion to decide crest level of the nearshore reef structure. In case of beach nourishment project the un-segmented row of tubes placed below MSL can be used as a dual purpose. Firstly, it acts as an offshore reef & helps the trapping of sediments during the downrush and secondly, as a barrier for the offshore movement of the existing nourished sand. The recurring periodic expenditure of the beach nourishment would also decreases after the beach stabilization within 2-3 years. Based on onshore-offshore movement or alongshore littoral drift, the solutions in the form of parallel offshore reef or perpendicular groyne field with sand-filled geotextile tubes are decided. The importance of site specific design with geotextile tubes in accordance with the needs & site conditions etc. are discussed in details with few case studies.

Optimisation of Direct Expansion (DX) Cooling Coils Aiming to Building Energy Efficiency

Efficient Air Conditioning (A/C) system is the key to reducing energy consumption in building operation. In order to decrease the energy consumption in an A/C system, a method to calculate the optimal tube row number of a direct expansion (DX) cooling coil for minimizing the entropy generation in the DX cooling which functioned as evaporator in the A/C system was developed. The optimal tube row numbers were determined based on the entropy generation minimization (EGM) approach. Parametric studies were conducted to demonstrate the application of the analytical calculation method. Optimal tube row number for different air mass flow rates, inlet air temperatures and sensible cooling loads were investigated. It was found that the optimal tube row number of a DX cooling coil was in the range of 5 - 9 under normal operating conditions. The optimal tube row number was less when the mass flow rate and inlet air temperature were increased. The tube row number increased when the sensible cooling load was increased. The exergy loss when using a non-optimal and optimal tube row numbers was compared to show the advantage of using the optimal tube row number. The decrease of exery loss ranged from around 24% to 70%. Therefore the new analytical method developed in this paper offers a good practice guide for the design of DX cooling coils for energy conservation.